Photodynamic therapy (PDT) is based on the administration of tumor-localizing photosensitizers followed by light exposure of the tumor mass. The photocytotoxic effects are mainly caused by the generation of singlet oxygen. Recently, PDT has been proposed for use in combination with anticancer chemotherapy with a view to exploiting any additive antitumor effect. We investigated the effect of PDT with photoactivated aluminum disulfonated phthalocyanine (AlS2Pc) combined with the antiblastic drugs Adriamycin (ADR) and cisplatinum (CDDP) on murine tumors. Mice bearing L1210 leukemia and P388 lymphoma were treated with ADR or CDDP and subsequently treated with PDT. Low chemotherapy doses were ineffective, but the combination of antiblastic drugs + PDT had a significantly additive antitumor effect. In conclusion, with this combined therapy we were able to greatly reduce the effective doses of antiblastic drugs, thus lowering their toxic effects on normal host tissues.